1. Field of the Invention
The present invention relates to devices for stimulating the growth of bone cells.
2. Description of the Related Art
Magnetic field therapy is often used to treat a variety of medical conditions. For example, the following U.S. patents teach various devices and methods of applying magnetic fields to treatment sites: U.S. Pat. No. 4,818,697 Liboff et al., issued Apr. 4, 1989, titled “Techniques for Enhancing the Permeability of Ions Through Membranes;” U.S. Pat. No. 4,932,951 Liboff et al., issued Jun. 12, 1990, titled “Method and Apparatus for Controlling Tissue Growth and an Applied Fluctuating Magnetic Field;” U.S. Pat. No. 5,059,298 Liboff, issued Oct. 22, 1991, titled “Method and Apparatus for Regulating Transmembrane Ion Movement;” U.S. Pat. No. 5,195,940 Baylink, issued Mar. 23, 1993, titled “Method for Increased Production of Growth Factor in Living Tissue Using an Applied Fluctuating Magnetic Field;” U.S. Pat. No. 5,330,410 Baylink, issued Jul. 19, 1994, titled “Method for Increased Production of Growth Factor in Living Tissue Using an Applied Fluctuating Magnetic Field;” and U.S. Pat. No. 5,792,040 Koeneman et al., issued Aug. 11, 1998, titled “Patient Interface Device for Generating Therapeutic Magnetic Fields.” Each of the above-listed patents is assigned to the assignee of the present application, and each is incorporated herein by reference in its entirety.
To apply a magnetic field to a treatment site, various wearer interface devices have been designed that place one or more magnetic field generating coils adjacent a body region that is to be treated. U.S. Pat. No. 5,139,474, entitled, “Medical Treatment Device with Self-Centering Securing Members,” illustrates one example of such a wearer interface device. The apparatus described therein engages a region of a wearer's body, such as a limb, with a pair of coils in opposed relation relative to the treatment region. This prior art apparatus has a relatively rigid shell comprising two rigid shell halves that are hinged together at a single hinge axis. The two shell halves pivot away from each other to a non-treating position and pivot towards each other in a treatment position. Means are provided for securing the shell halves together in the treatment position. One coil is disposed in each shell half and the pair of coils are used to generate the therapeutic magnetic field. That is, a voltage of a given amplitude and frequency is applied to the coils to induce a current and produce a magnetic field. Resilient securing members extend inward from the shell halves and have a flexible backing that applies a force radially from the shell halves. The resilient securing members deform outward to conform to the anatomy of the region to which it is applied.
U.S. Pat. No. 4,616,629, entitled “Coil Construction for Electromagnetic Treatment of an Afflicted Body Region,” describes a single-coil wearer interface device defining two U-shaped cavities. The two cavities are of unequal size, which permits the device to fit two different sizes of anatomical structures. Canadian Patent No. 1,314,941 discloses a treatment coil that is generally circular, having outwardly spiraling multiple strands of conductors.